Machine tool control system



1967 c. R. APTHORP, JR., ETAL 3'295416' MACHINE TOOL CONTROL SYSTEM Filed July 26, 1965 10 Sheets-Sheet l INVEN TORS CARL R. APTHORP, JR. FRANCISAFOSTER ROBERT L. NEKOLA THOMAS SAMAR M ZMM MW M Jan. 3, 1967 QR'APTHORPJR; ETAL 3,295,416

MACHINE TOOL CONTROL SYSTEM Filed July 26, 1965 1o Sheets-Sheet, 2

LEAD

SET sw's PULSE PG DIV.

ROTATION ll/l/l/I/ 104 10% 107 108 FEED PU LS E K T I I ///ll///Il/ DIV. "1/

LEAD g PULSE 01v. "{k"" T o h 112 R0 ATION \1 0 2 H Sw's' FIG. 5

INVENTORS CARL R. APTHORP, JR. FRANCIS Av FOSTER ROBERT L. NEKOLA THOMAS SAMAR Jan; 3, 1967 Filed July 26, 1965 c. R. APTHORP, JR., ETA

MACHI NE TOOL CONTROL SYSTEM PULSE 410 DIV.

] LEAD Fl 6 6 99 SET TAPER SW FACTOR W sw's I S 1 LEAD 11/ SET F" ROTATION 112 PULSE E DIV PG 108 FEED PULSE FIXED D N III/11. 107

110x PULSE Dw. LEAD 118 SET 1 sws Asa 4 S sw's L A D ON OFF REG. ROTATION 100 2 VAR Mo PULSE 107 v FEED v F'XED I PU L s E 116" Fl 6. 7 INVENTORS CARL R. APTHORP, JR. FRANCIS A. FOSTER ROBERT L. NEKOLA THOMAS SAMAR Jan. 3, 1967 APTHORP, ETAL 3,295,416

MACHINE TOOL CONTROL SYSTEM I Filed July 26. 1965 1o Sheets-Sheet 4 T0 ACCUM. 321

FIG I4 UP/ DOWN COUNTER- TEN'S' VI HI v. L I FIG. 80

VEMAX i=R c "LL. I 2

' INVENTORS mouocARL R. APTHORP, JR. SIABLEMV, FRANCIS A FOSTER ROBERT L. NEKOLA THOMAS SAMAR hmrmuEvOmM u u Jan. 3,1967 CQRAPTHORP, JR., ETAL MACHINE TOOL CONTROL SYSTEM F'il ed July 26, 1965 10 Sheets-Shet 5 wow hOr l l l I ll llillllilllLl r2 O Xvm X E532 mmv OOmP $2300 22 v k 2 nmwomwzw INVENTORS CARL R. APTHORP, JR. FRANCIS A. FOSTER ROBERT L. NEKOLA THOMAS SAMAR c. R. APTHORP, JR., ETAL 3,295,416

MACHINE TOOL CONTROL SYSTEM Jan. 3, 1967 10 Sheets-Shet 6 Filed July 26, 1965 I RNVENTORS CARL R. APTHORP, JR. FRANCIS A. FOSTER ROBERT L. NEKOLA THOMAS SAMAR 7 c. R. APTHORP, JR., ETAL 3,295,416

MACHINE TOOL CONTROL SYSTEM I Filed July 26. 1965 10 Sheets-Sheet v H H M Chg ZmXm mow TO rww w: .mC PDmC O INVENTORS CARL R. APTHORP, JR. FRANCIS A- FOSTER ROBERT L. NEKOLA THOMAS SAMAR V flaw M Jan. 3, 1967 r c. APTHORP, JR., ETAL 3,295,416

7 MACHINE TOOL CONTROL SYSTEM Filed July 26. 1965 v l0 Sheets-Sheet 8 swncu a4 DEENERGIZED SWITCH 34 DEENERGIZED INVENTORS CARL R. APTHORP, JR.

FRANCIS A. FOSTER ROBERT L. NEKOLA THOMAS SAMAR J 2 E I fWJA/ Jan. 3, 1967 c. R. APTHORP, JR., ETAL 3,295,416

MACHINE TOOL CONTROL SYSTEM Filed July 26, 1965 10 Sheets-Sheet 9 mmm 3555 2 5:5 mbzo 5:22. o

5.55m: ma s;

zm Suzi 5 has 5.5 $25.;

:2: m .zw $32591 was;

mew JEFS =6 5 5: E.

INVENTORS CARL R. APTHORP, JR. FRANCIS A. FOSTER ROBERT L. NEKOLA "THOMAS SAMAR M W M n- 1967 c. APTHORP, JR., ETAL 3295'416 MACHINE TOOL CONTROL SYSTEM Filed July 26. 1965 7 l0 Sheets-Sheet 10 mmm mum 5m .5300 JS INVENTORS CARL R. APTHORP, JR. FRANCIS A. FOSTER ROBERT L. NEKOLA THOMAS SAMAR BY w bw I 53m 303 Emu m United States Patent Ofilice Patented Jan. 3, 1967 3,295,416 MACHINE TOOL CONTROL SYSTEM Carl R. Apthorp, Jr., Shaker Heights, Francis A. Foster, Parma Heights, Robert L. Nekola, Chesterland, and Thomas Samar, University Heights, Ohio, assignors to The Cleveland Twist Drill Company, Cleveland, (line,

a corporation of Ohio Filed July 26, 1965, Ser. No. 474,549 Claims. (Cl. 90-1142) This invention relates to operating methods and control systems for machine tools, more particularly to such a method and system for a machine tool of the type having a cutting tool, means for holding a workpiece, and means for imparting compound movements to the cutting tool and the holder relative to one another in bringing them into operative relation and executing complex machine ope-ra-tions, such as spiral and helical fluting.

One aspect of the invention pertains to a method and system of the type described for multiple spiral or helical fluting operations requiring accurate rotation of the workpiece through angles exactly related to the axial movement.

Another aspect of this invention pertains to a method of and system for producing helical flutes of constant helical angles in a workpiece of varying cross-section.

Still another aspect of this invention pertains to a method and system for producing a varying lead on the interior or exterior surface of a workpiece in which the surface on which the cut is being made is of constant diameter.

In machine tools having compound movements referred to, it is essential that each element of this movement be executed in phase or timed relation with every other element and have the proper magnitude. For example, in milling a spiral or helical groove or flute in a workpiece, of circular section, such as in the manufacture of a twist drill, end mill or reamer, the workpiece, which may comprise a cylindrical or conical bar, is customarily mounted in the holder or spindle carried by the headstock on the table of a mil-ling machine; the tool is a rotary mill on a driven arbor which turns on a generally horizontal axis above and transverse or oblique to the spindle axis. The machine table reciprocates along a horizontal path parallel to the spindle axis to travel the workpiece in relation to the cutting tool. During the work or feed stroke of the table the spindle is turned in a constant or a varying relation to the feed rate so that the tool generates a helix or spiral about the workpiece and the helix has the desired lead, this operation being repeated, if multiple flutes are to be cut, as many times as required to provide the desired number of spiral or helical grooves or flutes on the workpiece. Between strokes of fluting operations the spindle is rotated or indexed to present the workpiece to the cutting tool at a starting position spaced angularly about the spindle axis from the preceding starting position, the extent of the rotation depending upon the number of flutes to be machined, that is, the circumferential spacing desired, and on the angular position of the workpiece where the cutting of the last groove ended. Before returning the table to starting position after a work stroke, it is customary to shift the table vertically relative to the cutting tool to withdraw the latter from the groove or flute just completed; this eliminates any contact between the cutting tool and the workpiece during the return stroke and permits a rapid rate of table travel to be used relative to the travel rate during the machining stroke.

In mechanical indexing systems of the prior art, the rotation of the workpiece is divided into a predetermined number of indexing steps as by a dviding head used with any one of a number of interchangeable indexing plates. Each of the plates has a number of holes arranged in a circle centered on the plate axis, each hole being adapted to receive a locating pin carried by a crank coaxial to the plate and geared to the member or workpiece through a single revolution in a series of steps equal to the number of holes in the plate circle. The spacing of the holes in the plate circle is varied in the different plates to provide indexing steps of diflerent lengths; each plate may be provided with a plurality of groups of holes arranged in concentric circles and with different numbers of holes in each circle. To change the indexing interval, the crank pin is changed from one circle to another; in some instances the indexing plate must be changed. This system of the prior art is cumbersome and inconvenient to use.

Various other systems have been devised for the purposes of achieving automatic or semi-automatic operation of machine tools and to control various and related cmpound movements of the parts such as the movements referred to above. Some of these'have used electrical pulse systems of various types, generally operating from the error signal of a closed loop servo motor; in some cases requiring an elaborate feedback and checking system to insure the correct execution of the commands. While systems heretofore devised have enjoyed a measore of acceptance and success, they have not been completely satisfactory because of the high cost, complexity, and difficulties in service and repair; more seriously, some priorsystems have been inflexible in that a changeover from one to another specification in machining a workpiece has been costly or time consuming or both. Troubles have also been encountered with feedback and other arrangements for error correction.

To machine a helical or spiral groove of a given constant lead in a workpiece of circular cross-section, the workpiece must rotate at an angular velocity directly proportional to the rate of feed or travel of the workpiece relative to the cutting or grinding tool in the direction parallel to the rotational axis of the work-piece and inversely proportional to the lead. Known mechanical helical generating systems employ a dividing head coupled to the feed screw through change gears. In the case where a constant helix angle is required on a tapered or conical workpiece, the angular velocity of the work spindle is directly proportional to the workpiece axial movement and inversely proportional to the product of the co-tangent of desired helix angle, twice the tangent of the angle which the periphery of the workpiece makes with the workpiece axis, 'and the distance from the vertex of the cone to the point of engagement between the workpiece and the cutting tool. The term conicity means the rate of taper of a conical workpiece per unit axial length.

To machine a helical or spiral groove of a variable lead in a workpiece of varying cross-section, such as a conical bar, the known systems are completely mechanical and employ a master former which has been pre-cut to the desired lead. A former pin is employed to follow the groove in the master and the workpiece is connected to the end of the master and is axially moved in response to the rotation of the master against the stationary former pin. This system requires a separate master for utting each difierent cross-section of workpiece. Each master must be hand-made by a toolrnaker, causing the masters to be relatively expensive and the requirement for numerous masters creates a storage problem.

To minimize the idle machining time during certain periods of the constant helix or variable helix cycles, the feed table is traversed at a rapid rate, as mentioned above. During such periods, the working parts in the dividing head are subjected to high stresses imposed by large forces built up through the gear train from the machine table lead screw and through to the workpiece driving spindle. These high stresses cause rapid wear and result in high maintenance costs.

It is therefore one of the principal objects of this invention to provide an improved method and system for controlling automatically, compound movements in a machine tool, more particularly to provide such a method and system for generating a helix or spiral of either constant or varying lead about a workpiece which may or may not have a constant cross-section.

It is therefore another of the principal objects of the invention to provide an improved method and system for controlling automatically, compound movements in 'a machine tool, more particularly to provide such a method and system for generating a helix or spiral of constant angle about a workpiece which workpiece does not have a uniform diameter.

Another object is to provide, in a control system fora machine having a rotary spindle which holds and transports the work relative to a cutting tool and a work feed drive capable of adjustment to different speeds for effecting such transport, an improved lead generating arrangement operating to maintain a predetermined relation between the rotational speed of the spindle and the transport drive and adapted automatically to vary the rotational speed of the spindle in synchronism with variationsin the transport drive so as to maintain a uniform lead in the machining of the Work regardless of the speed for which tional speed of the spindle and the transport drive and' adapted automatically to vary the rotational speed of the spindle 'in synchronism with variations in diameter of the workpiece and variations in the transport drive so as to naintain a uniform helix angle in the machining of the workpiece regardless of the speed for which the work feed drive is set in adjustment and of variations of such speed.

Another object is to provide a method and system of the :haracter referred to for generating a plurality of helices, ieriatim, of either constant or variable lead and spacing :hem angularly about the axis of the workpiece. This,

aspect of the invention is especially concerned with an arrangement of indexing the workpiece automatically in accordance with a preselected pattern, regardless of spacng, special consideration being given to ease of change- )ver in the setting up of a machine with respect. to the lumber of spiral grooves or flutes to be cut.

Other objects are concerned with the automatic indexng of a work holder in a machine tool so as to present :he work to the tool in ditferent positions for carrying out, ieriatim, related machining operations. One such object, nits broad aspect, aims to provide an indexing system and method wherein an incremental prime mover actuat- I ible by electrical pulses is connected to the work and the position of the work is altered by feeding a predetermined number of electrical pulses to such prime mover. More particularly, the invention is concerned with an indexing system wherein the prime mover is an electrohydraulic stepping motor or electrical stepping motor and the pulses for actuating it are fed through a register adapted to limit the pulses to a predetermined number and thereby control the extent of the indexing movement.

Another object concerned with the indexing of a workpiece in machine tool is to provide a system which permits the number of indexing steps to be readily changed; a further and more specialized object to provide such a system wherein the indexing drive takes the form of an incremental prime mover and the system readily is capable of dividing a predetermined cycle into many different parts. 7

A still further object of this invention is to provide .a readily adjustable machine tool control system for producing either constant or variable lead flutes, the accuracy of which system is repetitive and the error of which is negligible.

Another object of this invention is to provide a readily adjustable helix generating system for generating either a constant or a variable lead which permits the lead of the generated helix to be changed with ease, which system produces a constant helix angle in a conical workpiece or a varying lead in a workpiece of constant diameter.

Another object of this invention is to provide an open loop, completely digital, constant or variable lead helix generating and indexing system.

Yet another object of this invention is to provide a readily adjustable constant or variable lead helix and index generating system which is readily adaptable to numerical control by means of an independent master pulse source" which supplies a fraction of its output pulses to a stepping motor feed drive and supplies another fraction of its outputlpulses to a second stepping motor for rotating the spindle,

Other objects and features relate to certain combinations of parts and or process steps which will be evident in the following description of embodiments representing the best known mode of practicing the invention. This,

description is made in connectionwith the accompanying drawings forming a part of the disclosure.

In the drawings: FIGURE 1 is an outline front elevational view. of a machine tool embodying the invention. i

FIGURE 2 is a plan view, on the lines 2-2, .of FIG-. URE 1, showing the table portion of the machine tool.

FIGURE 3 is a detail view of a cam operated switch mechanism taken in the direction of the arrows 33 of FIGURE 1.

FIGURE 4 is a basic function block, schematic and fragmentary diagrammatic representation of a control sys-' tem known in the art.

FIGURES 5-7 are basic function block, schematicand fragmentary diagrammatic representations of embodiments of this invention.

FIGURE 8 is a wiring diagram of the index pulse generating unit used in the illustrativeembodiment.

FIGURE 8a is a voltage diagram showing how the frequency of the index pulse oscillator is varied.

FIGURE 8b is a general block diagram of a system used in the machine tool of FIGURE 1, and showing in solid lines the system of FIGURE 7 and showing in dotted outline the modifications required to employ the system of FIGURE 6.

FIGURE is a block diagram of a portion of a control system which can be substituted in the system of FIGURE 8b to produce the system of the type shown in FIGURE 5. 1

FIGURE 9 isa block diagram of one decade of the taper factor switches, counter, and comparing means of a pulse divider unit.

FIGURE 9a is a block diagram of one decade ofthe lead set switches, counter, storage register counter, and comparing means of a pulse divider unit.

FIGURE is a block diagram of a portion of the decision unit which determines that no acceleration or deceleration of the pulses are required.

FIGURE 11 is a block diagram of another portion of the decision unit which determines that acceleration or deceleration of pulses are required.

FIGURE 12 is a general block diagram of the acceleration-deceleration control unit.

FIGURE 13 is a block diagram of the tens decade of the up-down counter.

FIGURE 14 is a block diagram of the tens decade of the pulse multiplier unit.

FIGURE 15 is a detail circuit view of a steering circuit used in connection with certain counters.

FIGURE 16 is a block diagram of the stepping motor unit.

Typical operations performed by this machine which have been chosen to illustrate the invention are the milling of a cylindrical twist drill and the milling of a tapered workpiece to produce a tapered reamer, a tapered end mill or a tapered drill. A cylindrical drill is generally formed in a workpiece such as a bar or rod of cylindrical or conical stock. The lead of the grooves, that is, the length axially of the workpiece in which each groove makes one complete turn around the workpiece, may be fixed or variable and is exactly predetermined. The method and system for selectively achieving fixed or variable lead constimtes one aspect of the invention.

The grooves are usually evenly spaced around the workpiece. For example, if there are four grooves they are usually spaced 90 apart. Since the relationship between the angular position of the stock at the end of any cut and the beginning of the next cut varies widely, indexing of the workpiece to the correct position for starting the next cut requires a variably controlled operation. The method and system for achieving this constitute another aspect of the invention. Thus, the movements of the workpiece are divided into two different phases: first, helix generation; second, indexing. Helix generation is performed by a compound movement in which rotation of the workpiece is exactly related to feed of the workpiece.

In accordance with other aspects of the invention, a master variable pulse oscillator is employed and one of these two parts of the compound movement such as the feed is performed by an electro-hydr-aulic stepping motor feed driving means, the speed of which can be controlled by controlling the rate of pulses from the oscillator while the other part of the compound movement, i.e. the rotation of the spindle, is performed by a second stepping motor also driven by pulses from the oscillator fed at a fixed or variable related rate relative to the pulses fed to the first motor in a controlled manner to be described presently.

When employing a fixed pulse rate'on the second stepping motor, the relationship between pulses to the first and second stepping motors is a constant throughout the milling operation. This will produce a constant helix angle in a cylindrical workpiece or a variable helix angle on a tapered workpiece. If, however, a predetermined variable pulse rate is employed on the second stepping motor, throughout the milling operation, a variable lead will be produced in a cylindrical workpiece or a constant helix angle will be produced in a conical workpiece.

The feed rate of the workpiece is produced by an electro-hydraulic stepping motor which is driven by pulses from a master pulse generator of'variahly controllable uniform rate, while the rotary movement is produced, by a second stepping motor which receives its pulses from the same master pulse generator which turns the workpiece through a definite angle in response to each'pulse.

In accordance with a special feature of the prefer-red embodiment of the invention, the indexing of the workpiece is done by the same stepping motor used for helix generation, but the pulses which control the stepping motor during indexing are derived from an indexing pulse generator. This indexing pulse source may be of any convenient kind capable of delivering pulses of high frequency, such as an astable multivibrator.

In order to index the workpiece from the end of one cut to the point where the next cut is to begin, it is necessary to know the angular position of the workpiece when a cut is completed. Each pulse supplied to the stepping motor will rot-ate the workpiece through a definite angle. By knowing the angle between the finish of one cut and the beginning of the next cut it can be determined how many pulses of the stepping motor will be required to move the workpiece ahrough that angle. Inaccordance with the operation of the invention, the angular position of the workpiece is kept track of by a counter, called the main counter, which is pulsed by the same pulses that operate the second or spindle rotating stepping motor, in both the helix generation mode and the indexing mode.

For example, it may require 7200 steps of the stepping motor to rotate the workpiece through 360. If there are to be four indexes, the number of pulses required for one index will be 1800. If the number of pulses delivered to the first stepping motor during the generation of the first cut is 1440, the number of pulses to be supplied by the index pulse gen. (435) to bring the workpiece to the next index position will be 1800 minus 1440, or 360.

The number of pulses per second required to generate a helix varies directly with the feed rate and inversely with the helix lead. In the system to be described, as an illustrative embodiment of the invention, the rate of pulses for helix generation may vary from a minimum of 2.11 per second to 460 pulses per second. The maximum rate at which the particular stepping motor responds reliably from a stationary condition is p.p.s. but if it is properly accelerated, it can respond, without missing, to a pulse rate as high as 1000 pulses per second.

Means are provided to accelerate the motor and thereby the workpiece from a stationary condition to a maximum rate of rotation at a defined rate, such that there will be a correct response to every pulse. Thereby, the number in the main counter will truly represent the angular position of the workpiece at all times, and it is unnecessary to provide any other checking or feedback means to insure that the milling operation is proceeding in accordance with the conditions set up. On stopping the stepping motor, it is necessary to proceed through a deceleration operation if the motor is operating above its maximum limits. The pulse rate is therefore reduced at a defined rate from the maximum at which the stepping motor was being driven, to a rate at which the stepping motor can be stopped instantaneously.

In indexing, pulses are supplied at a maximum rate at which the stepping motor is able to follow without missing, if properly accelerated and decelerated. Special means of a simple nature are provided for accelerating and decelerating the pulses on indexing, as described in Patent 3,196,748. Means are provided to anticipate the arrival of the workpiece at the end of its indexing move.- ment, to begin deceleration, if needed, in time to permit the motor to be brought to a full stop when the workpiece has arrived exactly at the end of its indexing movement.

The control system of the present invention is described in relation to its application to a milling machine of known construction, indicated at M, FIGURE 1, the machine being of the type used to mill spiral flutes in a cylindrical workpiece W as in the manufacture of a twist drill or reamer. The milling machine M includes a table T supporting a headstock 1 in which a workholding member or spindle 2 is rotatably mounted on nti-friction bearings. The spindle is driven through iitable gearing by a stepping motor which forms part E a stepping motor unit S, referred to later in more etail, the motor unit being mounted on the headstock travel with it.

The table T, driven by a rotatable member or lead :rew 3, reciprocates along .a horizontal path, being Jitably supported as on parallel ways for sliding moon across a universal housing 10 carried by saddle 11. he housing is swingable about a vertical axis in adistment onv the saddle, as indicated by the position of 1e table T in FIGURE 2. The saddle is itself slidable 1 adjustment horizontally along a path normal to the lane of the drawing, FIGURE 1, on knee 12, as by leans of a hidden cross feed screw rotatably by hand- Iheel 14. The knee 12 is vertically slidable on dove- 1il ways of, and is carried by, the frame of the mahine M; a suitable vertically acting screw or hydraulic ssembly 15 footing on base 16 of the machine M is ctuatable to raise and lower the knee 12 between preetermined positions as determined by limit switches 7, 19 of a suitable electrical control system, later decribed. These limit switches are actuated at the deired points in the upward and downward movements f the knee and table assembly by vertically adjustable am plates 28, 29, respectively, which are carried by he knee 12. The table T is actuated for forward travel, r to the right as viewed in FIGURES 1 and 2, during t work or flute cutting stroke, when the head screw 3 s rotated in one direction and for reverse travel, or o the left as viewed in the same figures, during a reurn or recovery stroke, when the lead screw is rotated u the other direction. Limit switches 23 and 27 on he housing 10 connected in the electrical system re- 'erred to, are actuated at the desired limits of the orward and reverse movements of the table by hori- :ontally adjustable cam plates 31, 32 mounted on the ront side of the table T, to cause the table to stop, as vill appear. An electrohydraulic stepping motor 4 is :onnected directly to the lead screw 3 by means of which he rate of travel of the table T and therefore the cuting rate .or feed rate can be varied in accordance with pulses from the master variable pulse generator. The iced rate is set manually as by a feed change switch 24 mounted on a suitable control panel; a feed indizator dial 25 concentric to the axis of the switch 24 vis provided to indicate the feed rate for which the machine s set.

It is desirable to provide on and fast to the table T t suitable, steady rest or tail stock .18 for supporting the )utboard end of the workpiece W distal from the head itOCk 1.

A cutting tool such as a milling cutter is mounted )n horizontal ar bor 21 of the machine M. It is driven :onstantly in the usual manner when the machine is in mention to rotate at suitable speed about the axis of ;he arbor 21. Such axis is normal to the plane ofthe irawing and oblique to and spaced above longitudinal axis 22 (FIGURE 2) of the workpiece W about which :he latter turns and along which it reciprocates when the supporting table T is actuated for work and return strokes.

In the lowered position of the table, as determined by the setting of the cam plate 29 which governs the limit switch 19 the workpiece W is wholly below or removed from the relative path of the cutter, permitting return travel of the table to starting position with the cutter clearing the workpiece and without necessity for retracing the cutter through the flute or groove formed in the just completed cutting or fluting operation. The function of the switch 17 will be described later.

During the machining part of the machine cycle, the spindle 2 is turned by the stepping motor unit S at a controlled rate of rotational speed in order to generate a helix. This is accomplished by feeding pulses to the stepping motor unit in timed relation to the rate of table In order to achieve a high degree of accuracy in the relationship between the starting of the forward or work travel of the table T and the energization of the stepping motor unit S, a limit switch 34 is mounted on one end of the table T, the right-hand end as viewed in,

FIGURES 1 and 2, and is actuated by a finger 35 (FIG- URE 3) on a circular disc 36 fast on the end of the lead screw 3 which projects through the end of the table. Thus the switch 34 is actuated at a precise point in the rotation of the lead screw so that in machining multiple flutes in a workpiece, the generation of each succeeding helix is started with the table T in the same position as in the preceding machining operation. This feature contributes to the accuracy of the circumferential spacing of the several helical flutes and thus improves the quality of the work.

Travel of the table T to the right, as viewed in FIG- URES 1 and 2, is referred to herein as forward travel for the reason that the control and operation of the machine is described in relation to a method of ma.

chining in which the cutter 20 is initially brought into operational engagement with the workpiece W at the end of the latter remote from the spindle 2, each machining operation progressing from right to left from the outboard or distal end of the workpiece toward the end thereof held by the spindle. However, the invention is applicable to reverse machining in which, at the beginning of a fiuting operation the tableT is at its limit of movement to the right, as viewed in the figures just referred to, and travels from right to left during the machining operation. In such reverse machining the cutter 20 initially engages the workpiece W adjacent the left end of the latter which is held by the spindle 2 and travels toward the outboard or distal end. Moreover, the inventions can be used with either climb milling or conventional milling type of cut.

FIGURE 4 is a general block diagram of the. system for control of helix generation and indexing as disclosed in Apthorp et a1. Patent, 3,196,748, issued July 27, 1965, with respect to which the subject application constitutes an improvement. A constant speed motor 4 drives the lead screw 3 through the change speed gear box 5. The shaft 49 of a pulse generator or shaft encoder 52 is driven through gears, not shown, in gear box 5 so as to generate pulses at a basic rate determined by the selection of gears which control the feed rate.

of the workpiece in relation to the cutter.

the machine drive or lead screw, so that its output frequency will be a precise measure of the machining feed rate. One such generator is the Model 2710500 Optical Incremental Shaft Encoder, manufactured .by Dynamics Research corporatiom'stoneham, Massachusetts.

The pulses produced by the pulse generator are fed. to' a pulse divider which divides the pulses in accordance with the manually set lead set switches 99, in-

dicated only by the labeled block. The division is made in accordance with Equation 1 of the above mentioned.

patent. V

i This division is accomplished in accordance with the setting of the lead set switches and the divided pulses are fed through an amplifier to drive the stepping motor.

S. The driven shaft of stepping motor 5 rotatably drives the spindle 2 through a suitable gear train.

FIGURE 5 is an abbreviated function block diagram 9 of one illustrative embodiment of control system according to this invention. In this embodiment a master oscillator 104 delivers pulses to a variable pulse divider 105, the output of which is controlled in steps by a selector switch 106. The output pulses from the variable divider 105 are fed to the feed rate stepping motor 108 through an amplifier 107. The output pulses from the pulse divider 105 are also fed to a first pulse divider 100 and a second pulse divider 110. The rate of pulse division in pulse divider 100 is controlled by manually settable lead set switches 99 which in turn control a lead set register 109 and the output of the lead set register 109 in turn controls rate of pulse division of the pulse divider 100.

For the purposes of milling a constant lead, pulse divider 110 and its associated manually set taper switches 111 are not required. Accordingly, divider 110 is disabled. Assuming that a constant lead is being milled, the pulses from the pulse divider 105 are fed through the pulse divider 100 the output of which is controlled by the previously mentioned lead set switches 99 and lead set register 109. This output is fed through amplifier 112 to the spindle stepping motor, S. In milling a workpiece to provide a constant lead the lead set switches 99 are manually set and remain at this setting throughout the milling operation. The setting of the lead set switches 99 controls the set position of the lead set register 109 such that potentials are selectively provided on a plurality of output leads to the pulse divider which potentials control the rate of pulse division of the pulse divider 100. Thus, the pulse divider 100 will divide the pulses from pulse divider 105 at a constant rate and these constant rate pulses will be fed to the spindle stepping motor S.

If the embodiment of FIGURE is employed to produce a variable lead, divider 110 is enabled or turned on and the desired number called the taper factor is set into the manually setta'ble switches 111 which in turn selectively apply potentials over its output leads to the pulse divider 110. The pulse divider 110 is a constant divider the output pulse rate of which is determined by the potentials supplied from the taper switches 111, which divider output is fed to lead set register 109. These pulses from pulse divider 110 will constantly change number in the lead set register 109 such that the affect upon the pulse divider 100 is to change the pulse division rate at a rate determined by the rate of pulses being fed from the pulse divider 110 to the lead set register 109. Thus the variable rate output pulses from pulse divider 100 will be fed through the amplifier 112 to the spindle stepping motor S to provide a variable taper on the workpiece. If the workpiece being cut during this operation is cylindrical in cross-section the resultant cut is a variable lead. If, however, the workpiece is tapered, the result is a constant helix angle provided, of course, that the taper switches are properly set for the connicity of the workpiece.

FIGURE 6 is an abbreviated function block and fragmentary schematic diagram of another illustrative embodiment of this invention which may be employed for cutting flutes or grooves having either constant or variable leads. In FIGURE 6 the master oscillator 104 has its output connected to a pulse divider 100 and a second pulse divider 105. The output of pulse divider 100 is fed through an amplifier 112 to the spindle stepping motor S. The output of pulse divider 105 is fed through an amplifier 107 to the feed stepping motor 108. The output of pulse divider 105 is also fed to a pulse divider 110 the output of which is determined by a group of taper factor switches 111 which may be manually set. The output of pulse divider 110 is fed to a lead set register 109 which is initially set by a group of lead set switches 99. The output potentials of the lead set register 109 determine the rate of pulse division by the pulse di- 10 vider 100. The pulse divider 105 is provided with a manually settable switch 106 which combination of pulse divider 105 and switch 106 are identical to those previously described in connection with FIGURE 5.

For producing a constant helix angle, the feedback loop through divider 110 is disabled and the pulses from the pulse generator 104 are fed to the pulse dividers and and then in accordance with respective pulse division rates pulses are fed to the stepping motors S and 108 respectively.

If a variable helix angle is desired, the feedback loop is employed and the pulses from the pulse divider 105 are fed through the pulse divider to the lead set register 109. The lead set register 109 produces at its output a set of binary potentials of constant magnitude which are stepped from lead number to lead number. These output potentials cause pulse divider 100 to deliver output pulses of constant magnitude and preselected varying repetition rate proportional to the change in workpiece diameter. These varying rate pulses are fed to the spindle stepping motor S. Thus in producing the variable lead a. predetermined relationship is established between the taper factor switches 111, the lead set switches 99 and the pulse divider setting switch 106.

In the instance of a constant helix angle, the control system of FIGURE 6 will produce a constant lead in a cylindrical workpiece and a varying lead in a conical workpiece. If, however, a variable lead is employed, a varying helix angle will be produced in a conical workpiece, assuming, of course, that the rate of variable lead is in proper relationship to the connicity of the conical workpiece.

FIGURE 7 is a combined function block and fragmentary schematic representation of a preferred embodiment of control system according to this invention. In

FIGURE 7 a variable master oscillator feeds pulses at a predetermined rate to a pulse divider 100 and fixed pulse divider 116. The output pulses from the master oscillator 115 may also he fed through and AND-gate 118 to a pulse divider 110, which pulse divider is controlled by taper factor switches 111. The control of the condition of an' AND-gate 118 is achieved by means of a switch 120. When the switch is in its right-hand position, ground is connected to AND-gate 118, and this gate is effectively closed. If, however, switch 120 is in its left-hand contacting position, a negative potential is applied to AND-gate 118 and the pulse from the variable master oscillator 115 will be fed through the AND-gate 118 to the pulse divider 110. These pulses will be divided by divider 110 at a rate in accordance with the setting of the taper factor switches 111 and fed to the lead set register 109. The lead set register 109 operates in the manner described with respect to FIGURE 6 and Will continuously vary the pulse division rate of pulse divider 100. This variable pulse rate will then be fed through amplifier 112 to the rotation stepping motor S which rotates the spindle 2. Thus the system depicted in FIG- URE 7 is capable of producing a constant lead when the switch 120 is in its right-hand or ofi position or is capable of producing a variable lead when the switch 120 is in its left-hand or on position. When this system is employed to operate on a cylindrical workpiece the constant lead arrangement produces a constant helix angle. If, however, a conical workpiece is employed then a varying helix angle is produced. In the instance of a variable lead, if a cylindrical workpiece is employed, a varying lead will be produced in a workpiece. With a variable lead and a conical workpiece, a constant helix angle will be cut in the workpiece, again assuming proper connicity. As used in the specification, varying rate means a linearly varying pulse repetition rate. Varying lead as employed to produce a constant helix angle on a conical workpiece means a lead which changes at a rate corresponding to the change in diameter of the workpiece.

The details of lead set switches 99, lead set register [09 and pulse divider 100 are shown in FIGURc 9a. As shown therein, the pulse divider 100 comprises a three-decade binary code decimal up counter as shown in Hand Book of Semiconductor Electronics, Lloyd F. Hunter, VIcGraw-Hill, 1956, Chapter 15, Section 5 6. This counter will count up to any number that is in the lead set regis- ;er and will then in conjunction with a coincidence deection network issue an output pulse. The output pulse s fed thru required logic to stepping motor S. The same )ulse delaped, resets the pulse divider counter thus makng the division continuous. The counter is thus able .0 continuously divide the pulses fed to it, by any number n the lead set register. The lead set register is preset with the lead number thru the lead set switches. The twitches are coupled through suitable gating to the preiettable up counter called the lead set register, in turn he readout of the register is coupled to the pulse divlder :ounter by a coincidence detecting network. One decade Ithe least significant one) of the four-part system comarising switches, counter, coincidence detecting network, 1nd lead set register is shown in FIGURE 9a.

The pulse divider decade is composed of 'four bistable nultivibrators (flip-flops) MV1, MVZ, MV3 and MV4, :onnected in a RST manner (Reset, Set, Trigger), as :hown in National Bureau of Standards Circuit No. 12, nultivibrator, bistable (150 kc.), and two diode resistance kND-gates 121 and 122 similar to those illustrated in Logical Design of Digital Computers, Montgomery ?hister, Ir., John Wiley & Sons 5th printing( April 1960, rages 22 and 23. The flip-flops and AND-gates are com- )ined to form a four-bit, binary coded decimal up counter vhich counts in binary form through 9 and resets on the enth pulse. In each bit position of the counter a negative 'oltage on the right side indicates a T while anegative oltage on the left side indicates a 1 in that position. In he reset state of the counter, the four stages all have iegative voltage output on the right side, as indicated by he 1 in the box on that side and ground voltage on the )utput of the left side as indicated by the on the left tide. The counter is in a zero state.

The basic operation of the single decade of the pulse livider counter shown in FIGURE 9a will be described, vith reference to Table I, assuming that the counter tands at zero and that pulses f are fed to the T terminal of the one-bit flip-flop 110. The one to zero ransition of the first pulse into the counter changes.

lip-flop MV1 to the 1 state; that is, it has a negative oltage on its left output as indicated by the 1 next to this utput; 1 and 1 above the flip-flop have the significance hat negative voltage at the left output shows that the lip-flop is at a binary one, while a negative voltage at he right output means the flip-flop is at I or binary 0 s ow AND-gate 121 is enabled because both of its inputs 1 and 8) are in the 1 (negative) state. The 1 output of he gate is fed to the T input of the two-bit flip-flop 111. \fter the first pulse, the states of the flip-flops are as hown in Table I, on the line identified by pulse No.1,

ind the output of the counter 1s a bmary 1.

TABLE I 8 4 4 2 2 1 1 No. of

Pulse 0 1 0 1 0 1 o 1 0 0 1 0 1 0 1 1 0 1 0 1 0 1 1 0 0 1 2 0 1 0 1 1 0 1 0 3 o 1 1 0 0 a 1 0 1 4 o 1 1 0 0 1 1 0 5 0 1 1 0 1 0 0 1 6 0 1 1 0 1 0 1 0 7 1 0 0 1 0 1 0 1 s 1 0 0 1 0 1 1 0 9 0 1 0 1 0 1 0 1 10 The second pulse changes flip-flop MV1, the one-bit, to the zero of 1 state and AND-gate 121 is disabled. The one to zero transition of this AND-gate, applied to the T input of flip-flop MVZ switches the flip-flop. After the second pulse the condition of the four flip-flops is as shown in Table I.

As further pulses are transmitted to the T input of flipflop MV1 the stages of the binary counter go through the normal binary progression in obvious manner until the eigth pulse. At the time this pulse arrives the state of the flip-flops is as shown in Table I after the seventh pulse. The eight pulse switches the one-bit flip-flop to the reset state and the two and .four hits follow in the normal progression. The 1 to 0 transition from the left output of the flip-flop MV3 applies a pulse to the set input of flip-flops MV4, switching it to the set or one state. AND-gate 121 is not disabled by the 0 output from the I terminal of flip-flop MV4, while the AND-gate 122 is partially conditioned by the 1 input from the 8 terminal of flip-flop MV4. At this time the flip-flops stand in the condition shown after pulse 8 in the table.

The ninth pulse changes flip-flop and its 1 state is transmitted to AND circuit 121, which does not respond, because of the I condition on its right-hand input. AND gate 122 is enabled by the same 1 pulse flip-flop MV1, left output, and sends a 1 to the T terminal of flip flop MV4. The four-bit position now stand as shown in the table after pulse 9. p

The tenth pulse resets flip-flop MV1, with no effect on change from AND-gate 122. The four stages now stand as shown after pulse 10 in Table I.

The 8 output of flip-flop MV4 is connected to the input of the one-bit flip-flop of the next higher order decade of the counter (not shown). Thus, the return of flip-flop MV4 to the reset state on the tenth pulse sends a one-tozero transition pulse to the one-bit flip-flop of the next higher order decade and adds a one to that decade. A similar coupling is provided between the second and third order decades. The lead set switches 101 are manually set to a pre-selected lead number which in turn is set into the three-decade lead set register. The lead number in the lead set register determines the number to which the three-decade pulse divider. counter will count before an output signal is issued. To describe the switches, only the least significant decade of the lead set switches is shown in FIGURE 9a. Each index of the switch corresponds to a unique decimal number between 0 and 9. The ordinal Weight assigned to the number is determined by its position from left to right, that is, whether it is in the 10 10 or 10* decade.

The switch has four wafers 130, 131, 132 and 133 ganged on a single shaft and is so wired as to produce a binary number in the 1-2-4-8 form, reading from left to right in the wiring diagram, equal to the decimal num- The arms 134 pertainingto the respective switch wafers are coupled through gating to the set input terminals of the lead set register FFs, MVS, MV6, MV7 and MV8. The lead set register being a three decade binary coded decimal, presettable, up counter whose counting operation is identical to the pulse divider counter (100) just described. In addition the register can be preset by a pulse moving through and gates A1A2-A3A4 controlled by the lead set switches. Furthermore, when f pulses are fed into the counter on line 143 the counter will count up these pulses thereby changing the least significant digit of the lead number in the register by one for each pulse. Thus it can be seen that the lead number can be changed by pulses from the pulse divider which is being controlled by the taper factor switches. The readout of the lead set register is coupled to the corresponding bit positions of the pulse divider counter by the coincidence detector network one position of which will now be described.

Taking the wafer pertaining to the bit position 2, at the left end of the row, it will be noticed that the index terminals of the water are wired in overlapping alternate arrangement, all of the odd numbered terminals being wired to 12 volts, which represents a binary 1, while the even terminals are all wired to volts, representing a binary 0, or 1. Thus, with the setting shown, the arm of this section of the switch connected to l2 vol-ts.

The switch partially enables the first bit AND-gate (A-1) and when a pulse is fed to the gate at the start of a feed cycle, the pulse moves through the gate and presets the first bit of the storage register counter to a 1. Other bits of the register could be preset providing that their respective AND-gate were partially enabled by the lead set switch.

In the related position of the pulse divider counter, the 1 output is wired through diode 135 to resistor R1, while the 1 output terminal is connected through diode 136 to resistor R2. Resistor R1 is connected directly to the 1 output of the first bit of the lead set register counter, while the resistor R2 is connected to the 1 output of the same bit.

The junctions of diode 135 and resistor R1, and of diode 136 and resistor R2, are connected through respective Wires and reversely directed diodes 138 and 139, respectively, tothe end of a resistor 140 which has +6 volts at the other end and is center tapped to the base of a transistor 141.

With the setting as shown in FIGURE 9a, the level of the voltage on both sides of R2 is 0 and therefore the voltage at A and at the cathode of 139 will be positive with respect to the plate, thereby back-biasing the diode, allowing only leakage current to flow through it. The voltage level across R1 is a logic 1 because both sides of the resistor have the same voltage level, namely l2 volts. Therefore, the level at point B will be a 1. This will make the cathode of 138 negative and the diode will be forward biased to conduct; the voltage at C will be approximately at the 1 level, thus the inverter141 will have a 1 on its base and its out-put to AND-gate 123 will be 0.

When the next pulse triggers the binary counter to the 1 state, there will be coincidence between the register setting and the state of flip-flop MV1. Diode 136 will have a 1 on its plate and will be back-biased, therefore, the level at A will be approximately I or 0 volts. Diode 135 will have a 0 on its plate and will be forward-biased, therefore, the level at B will be approximately 0 also. Now, there are zeros on the cathodes of diodes 138 and 139 and they are back-biased.

If these were the only two connections affecting the voltage on the base of the inverter, it would now change to a non-conducting state and a 1 would be delivered to the AND circuit 123. However, the condition of the inverter 141 is affected by the same comparing circuits of all bit positions of all three decades; it is necessary for all of the diodes such as 139 and 138 to be back-biased, before the voltage on the base of the inverter can rise to change its condition to put a 1 on its output. When this occurs, the same pulse which caused the last change 14 of the counter, and which is delayed by delay circuit 142, provides the other input to AND circuit 123 and causes a 1 output. The same pulse passes through OR circuit 124 to reset the counter.

The output from AND circuit 123 occurs after a number of f pulses equal to the number set in the lead set register has been delivered to the counter. Thereby, the frequency of the pulses issuing from the pulse divider 190 is such as to cause the stepping motor to turn at the correct rate to generate a helix with the desired lead, subject to further conditions to be described next.

PULSE DIVIDER AND TAPER FACTOR SWITCHES The details of taper factor switches 111 and pulse divider are shown in FIGURE 9.

The pulse divider 119 comprises a three-decade binarycoded decimal up counter and a coincidence network. This counter will count up to any number determined by the taper factor switches 111 and will then in conjunction with a coincidence detection network issue an output pulse. The counter is thus able to divide the f pulses fed to it, by a number set up on the switches. The switches are coupled to the counter by a coincidence detecting network. One decade (the least significant one) of the three-part system comprising switches, counter and coincidence detecting network is shown in FIGURE 9.

The decade is composed of four bistable multivibrators (flip-flops) MV9, MVltl, MV11 and MV12, identical in structure and operation to the corresponding flip-flops MVI, MV2, MV3 and MV4 in FIGURE 9a.

The three-decade storage system, the taper factor switches 111, determines the number to which the threedecade counter will count before an output signal is issued. Again, only the least significant decade of the taper factor switches is shown in FIGURE 9. Each index of the switch corresponds to a unique decimal number between 0 and 9. The ordinal weight assigned to the number is determined by its position from left to right, that is, whether it is in the 10 10 or 10 decade.

The switch has four wafers a, 131a, 132a, 133a ganged on a single shaft and identical in structure and operation to wafers 130, 131, 132 and 133 of FIGURE 9a.

In the position of the counter, corresponding to the indicated position of wafer 130a, the I output is wired through diode 135a to resistor Rla, while 1 output terminal is connected through diode 136a to resistor R2a. Resistor Rla is connected directly to the arm of the switch, while resistor R2a is connected to the arm through an inverter 137a. V

The junctions of diode 135a and resistor Rla, and of diode 136a and resistor R2a, are connected through respective wires and reversely directer diodes 138a and 139a, respectively, to the end of a resistor 140a which has +6 volts at the other end and is center tapped to the base of a transistor 141a, which acts as an inverter.

With the setting as shown in FIG. 9, thelevel of the voltage on both sides of R2a is 0 and therefore the voltage at A and at the cathode of 139a will be positive with respect to the plate, thereby back-biasing the diode, allowing only leakage current to flow through it. The voltage level across Rla is at logic 1 because both sides of the resistor have the same voltage level, namely l2 volts. Therefore, the level at point B will be a 1. This will make the cathode of 138a negative and the diode will be forward biased to conduct; the voltage at C will be approximately at the 1 level, thus the inverter 141a will have a l on its base and its output to, AND gate 123a will be 0.

When the next pulse triggers the binary counter to the 1 state, there will be coincidence between. the switch setting and the state of flip-flop MV9. Diode 136a will have. a 1 on its plate and will be back-biased, therefore, the level at A will be approximately 1 or 0 volts. Diode 135a will have a 0 on its plate and will be forwardbiased, therefore, the level at B will be approximately also. Now, there are zeros on the cathodes of diodes 138a and 139a and they are back-biased.

If these were the only two connections affecting the voltage on the base of the inverter, it would now change to a non-conducting state and a 1 would be delivered to the AND circuit 123a. However, the condition of the inverter 14111 is afiected by the same comparing circuits of all bit positions of all three decades; it is necessary for all of the diodes such as 139a and 138a to be backbiased, before the voltage on the base of the inverter can rise to change its condition to put a l on its output. When this occurs, the same pulse which caused the last change of the counter, and which is delayed by delay circuit 142a, provides the other input to AND circuit 123a and causes a 1 output. The same pulse passes through OR circuit 124a to reset the counter.

The output from AND circuit 123a occurs after a number of f pulses equal to the number set in the taper factor switches has been delivered to the counter. Thereby,

the output frequency rate of the pulses issuing from the" pulse divider 110 is such as to change the number in the lead set register 109 to correspond with the lead number required to generate the desired helix angle.

DECISION UNIT The pulses that step the motor are counted to record the angular position of the workpiece. In the illustrative machine being described, each pulse rotates the workpiece 6- of a turn. If the stepping motor does not move a step for each pulse it receives, the accuracy and the repetitive ability of the helix generating and indexing system are destroyed. One limiting characteristic of the stepping motor is that it cannot be started or stopped instantaneously at pulse rates greater than 100 pulses/ second; however, it can accurately step at rates up to 1000 pulses/ second if it is accelerated from 100 pulses/ second, or less,

to 1000 pulses/ second and decelerated from 1000 pulses/ second to 100 pulses/second, or less. Should it'be subw ject to excessive starting pulse rates, it will react erratically; either it will not respond to each pulse, or it will not start at all. Since the system requires the motor to operate over a pulse range of 2.11 through 460 pulses/ second, malfunction could occur in the range between 101 and 460 pulses/ second. L

The pulse rates, therefore, can be divided into two This could be the case if, for example, the feed" acceleration-deceleration procedure. The latter unit switches the pulses of f frequency directly to the stepping motor, if the pulse rate f is below 100 p.p.s., but if'it is greater than 100 p.p.s., the acceleration-deceleration control unit operates to alter the pulse train to conform to the motor response capability. The decision unit 200 consists of two AND gate matrices, one matrix, FIGURE 10,

detects settings calling for pulse rates below 100 p.p.s. and provides a signal to direct pulses of frequency f from the pulse divider 100 to the motor; the other matrix, FIG- URE l1, detects settings requiring pulse rates greater than 100 p.p.s. inhibits pulses directly from the pulse divider 100 to the motor, and engages the acceleration-deceleration control unit 300, which alters the pulse train-to.

tacts of the feed set switch 90 The arm 91 of this switch is selectively connected to these contacts by rotating the pulse rate switch dial arm 24. The arm is supplied with current from a 12 volt source and, according to its position, partially conditions one of the six AND-gates of FIGURE 10 labeled 220-225. A seventh AND-gate 226' is not affected by the feed control switch group.

The AND-gate 221-225 are additionally partially conditioned, and AND-gate 226 is partially conditioned, by inputs from another set of six wire 230-235, as shown, connected to extra sections of the units and tens decades of the lead-set dial switches 102 and 103. The connec-- tions of the wires to these extra sections of the switches 102 and 103 is such as to generate the inputs, on the respective wires shownby legends in FIGURE 10. The

AND circuit 220 is not afiected by any wire of the group. 230-235. Each of the AND circuits 220 to 226 isadditionally partially conditioned by an input on wire 240 which comes from' a monostable multivibrator (not shown) that is triggered by switch 34 (FIGURE 3) when it is de-energized, that is, released by cam 35.

The following is an explanation of the operation of the matrix 426 of FIGURE 8b shown in detail in FIGURE 10, that determines when no acceleration or deceleration is required.

lead were set on the switches 101 at 04.0 that is, 4"/rev.v

The pulse rate f would then be 92/ sec.

But if the pulse rate f is greater than 100 p.p.s., it is necessary to go through the acceleration procedure, as previously stated, in order to bring the stepping motor up to a speed at which it will respond to every pulse of the selected pulse rate f Likewise, the deceleration procedure must be followed before stopping the stepping motor at the end of the cut.

The decision as to what pulse rate is required to generate the particular helix selected, is made by the decision unit shown at 200 in FIGURE 5 and in greater detail in FIGURES 10 and 11. This unit is under the control of the lead' set switch group '99 and a feed set switch group 90, the switch arm 91 of which is fixed to the shaft 24 of pulse rate setting switch 25. The decision unit 200, in turn, sets up a unit 300, which directly controls the The matrix detects that the pulse rates are less than p.p.s by combining pulse rate setting with a lead setting such that theminimum lead setting in therange pertaining to the particular wire 230-234 will not require pulse rates higher than 100 p.p.s. When'a condition, for example, a pulse rate setting of 3 "/mi.n. and a lead which is equal to or. greater than 4"/rev. have been set on the proper dials of the machine, the pulse rate to the motor is approximately 92 p.p.s., 91.375 p.p.s., as can be determined by applying the formulas previously referred to. It can be seen from FIGURE 10 that AND gate 223 is partially enabled, by an input from wire 213 pertaining to 3 min. of the feed rate set switch and wire 232 pertaining to equal to or greater than 4' '/rev., on the lead-set switches. The AND gate 223 is finally conditioned by an input on wire 240. The signal from AND gate 223 passes through OR gate 241 and by wire 242,.to set flipflop 301 (FIGURES 8b and 12). The 1 condition on the left side of this flip-flop is communicated by wire 302 to partially condition AND gate 303 to allow pulses of frequency f to be transmitted through OR gate 305 directly to the stepping motor unit S, a detailed descriptionof which will follow later. The zero condition on the right side of flip-flop 301 is communicated through wire 306 to AND gate 304, disabling this AND gate and blocking pulses from control unit 300.

.pulse rate.

1 7 ACCELERATION AND DECELERATION REQUIRED If the combination of settings of the lead set switches and the pulse rate switches is such as to require a pulse rate greater than 100 pulses per second, the decision unit 200 will receive a setting such as to require the pulses to pass through the pulse multiplier section of the acceleration-deceleration control unit 300, whereby their rate will be reduced to a frequency below 100 pulses per second initially and built up at a predetermined speed to the full rate delivered from the pulse divider 100. At this time the pulses will be switched, as will be described so as to be fed directly from the pulse divider 100, for the duration of cutting of the helix. When the helix has been completed and the cutter withdrawn from the workpiece, the acceleration-deceleration control unit 300 will come into play again to reduce the pulse rate from the f frequency down to a frequency below 100 pulses per second, at which time the stepping motor can be stopped instantly.

To explain the action of the acceleration and deceleration of pulses, an example will be taken of a 1.5/rev. lead and a %/min. pulse rate, which calls for a pulse rate of 460 p.p.s., well over the instantaneous startingstopping rate of the motor.

The higher pulse rate required in this example is detected by the second switch matrix of the decision unit 200 shown in FIGURE 11. This switching matrix resembles the one shown in FIGURE 10 previously described, except that the inputs to the sets of wires leading to the various AND gates are different, as shown by the legends at the ends of these wires. In this case, of the feed rate wires, only wires 211215 are used, which extend from the contacts of switch group 90 in the range from l /s"/min. to 5%"/min. The lead-set switch wires include wires 230, 231, and 233 shown in FIGURE 10, and three additional wires 260, 261 and 262, with the inputs shown in the legends.

The outputs from the AND gates 265-276 lead through three OR gates 277-279, in the pattern shown. The OR gates feed respectively AND gates 280, 281, and 282. Inverters 283 and 284 permit AND gates 270 or 271 to be partially conditioned when AND gates 265 or 266 are not fully conditioned, as will be shown in the chosen example. The combination of an input on wire 260, partially conditioning AND gate 270, leads to full conditioning of that AND gate by the inverted output of AND gate 265, due to the absence of an input on wire 214. Outputs on the lines 285-288 serve to preset numbers in storage elements of the acceleration-deceleration control unit 300, which will not be described.

ACCELERATION-DECELERATION CONTROL UNIT In order to insure a motor response step for each input pulse, pulse rates in excess of 100 pulses per second must be altered before being used to start and stop the motor, as previously stated. The acceleration-deceleration control unit 300 (FIGURE 81)) is provided to produce a pulse train that starts at a rate below 100 pulses/ second and then increases 1% steps to the final desired Also at the end of the cut, this control unit decreases the pulse rate in 1% steps to a rate below 100 pulses/second, at which point the motor can be instantaneously stopped. Thus, the motor is accelerated when it is started and decelerated before it is stopped in a manner that insures reliable operation.

The acceleration-deceleration control unit 300 (FIG- ures 8b, 12, 13, and 14) includes a two-decade pulse multiplier unit 310, 311 (FIGURE 12) with two inputs: (1) A varying two-digit numeric quantity produced in a settable up-down counter 312, 313; and (2) a pulse train from a pulse generator 104, 'shown at the left side of FIGURE 12, controlled by f pulses from the pulse divider 100. The output is a new pulse train which is the product of the pulse divider-rate and the number in the up-down counter, which product is always less than pulse per second in the starting setting of the updown counter.

The-pulse generating system which'is the second input to the pulse multiplier unit 310-, 311 includes a pulse doubler 150, which receives pulses at the rate of f from OR gate 68 of the pulse generating unit 104. The output 21 of unit is fed to one input of AND gate 151; these pulses have a reptition rate at least 20 times that of the highest possible rate of pulses f at any time, for a reason to be described later. The other input to AND gate 151 is from the set side of a flip-flop 152, the S iuput of which is fed by f pulses from the pulse divider 100. The output of AND gate 151 is fed to a divide-by- 10 counter 153, the output of which is returned to the R input of flip-flop 152.

The circuit, as so far described, operates in the following manner: Assuming the flip-flop 152 to be in the reset condition, the next f pulse will'switch it to the set condition, producing a logic 1 state on its output and partiallyconditioning ANDgate 151. Ten 2f pulses will now pass to counter 153,-which will issue an output pulse on receiving thetenth pulse and reset flip-flop 152. The same sequence occurs for each f pulse.

Each group of ten 2f pulses passes line 154 to one input of an AND gate 315, While each single pulse from counter 153 is fed by line 155 to one input of an AND gate 316 at the rate )3; thus the groups of ten pulses are sent to AND gate 315 at the same rate per group as the single'pulses to AND gate 316. The AND gates 315 and 316 are controlled by a1 condition at the output of the reset side of a flip-flop 301, over line 156, when it is in the reset state.

THE UP-DOWN COUNTER The up-down counter comprises a ones decade 312 and a tens decade 313. These decades are similar binarydecimal counters, one of which will be described in detail later. Accordingly, each has a group of four outputs of weighted values 1, 2, 4, 8 as indicated, numbered 317 and 318, respectively, which extend to the pulse multiplier decades 310 and 311, respectively. Unit pulses are fed to decade 312 from OR gate 323, in a manner to be described, and on counting ten such pulses decade 312 passes a carry pulse over line 157 to the input of decade 313. V w

The two decades 312 and 313 are coupled by groups of lines to the decision unit 200. While four input lines to each decade are shown in FIGURE 12, since any desired 2-digit number could be set in the up-down counter, in the present example, as will be seen by referring to FIGURE 11, only the one-bit line 286, the two-bit line 285, and the four-bit line 287 carry pulses to the tens decade 313, while the line 288 leading to the one-bit input of the ones decade is also connected to the lines 289 and 290 leading to the two-bit and four-bit input to the ones decade, respectively. I

In the chosen examples, the matrix shown in FIGURE 11 will be set up by the pulse rate set switches and the lead set switches in the manner previously described, to generate an output from AND gate 281 on line 286, when switch 34 is tie-energized. The output pulse on line 286 will set up a one in the tens decade 313 of the up-down counter, while the direct output on line 288 will set up a binary 7 (l, 2 and 4 bits) in the ones decade 312 of the up-down counter. The structure and operation of the up-down counter will be described in detail later but for the present a more general description of the acceleration-deceleration unit 300 will be continued.

Both pulse multiplier decades 310 and 311 are so constructed, as will be described in detail presently, that their number of output pulses is controlled by the two binary numbers, herein referred to as K and K standing on the groups of lines. 317 and 318, respectively, which connect the decades of the :updown counters to the corresponding pulse multiplier decades. From AND gate 315 decade 311 receives ten pulses for each f pulse issuing from the pulse divider 100. The 1 which was preset in the tens decade 313 causes the pulse multiplier decade 311 to issue pulses H in accordance with the equation:

The pulse multiplier decade 310, which receives from AND gate 316 one pulse for every f pulse, issues pulses J in accordance with the equation:

These pulses from the two decades of the pulse multiplier are supplied, in different time phases, due to a delay unit 319, through OR gate 320 to an accumulator decade 321. The pulses are accumulated at the rate of 460 322=782 p.p.s. They are divided by ten in the accumulator so that the pulses issue from the accumulator 321 at the rate of 782/l=78.2 p.p.s.; this is a rate of pulses which the stepping motor can handle without inaccuracy of response. Due to the reset state of flip-flop 301, whenever acceleration is called for since no setting pulse has issued on line 242 as described, a 1 condition on line 306 partially conditions AND gate 304 and the pulses from the accumulator 321 .pass through AND gate 304 and OR gate 305 to the stepping motor unit S.

The pulse rate is to be accelerated in 1% steps; consequently, means are provided to increase the number in the up-down counter by 1 in response to the delivery of every four pulses from the accumulator 321. The same pulses which are passed through AND gate 304 and OR gate 305 to the stepping motor unit are delivered to a divide-by-four counter 322, which issues a pulse after every four pulses which it receives. The pulse from the divide-by-four counter passes through OR gate 323 to the ones decade 312 of the up-down counter. Thus, after four pulses to the stepping motor unit the count in the ones decade 312 is increased from 7 to 8.

The pulse multiplier decade 310 riowtggpasses 8 pulses for each pulses received from AND-gate 316. Thus, it delivers 368 pulses per second, which, when added to the 460 pulses per second from decade 311,*make a total of 828 pulses per second. The pulse rate to the stepping motor is now 82.8 p.p.s.j That is to say, the number of pulses per second has been changed by 82.8 minus 78.2 equals 4.6, or 1% of 460 p.p.s.

When the units decade 312 passes from 9 to 0 it transmits a carry pulse to the tens decade 313 over line 157, changing the output from this decade to a binary 2.

The binary 9 outputs of line groups 317 and 318 are coupled by lines 324 and 325 to an AND gate 326, which has a fifth input line 327a which supplies a logical 1 to AND-gate 326 whenever the up-down counter is set to count up. Thus, when the lines 324 and 325 both supply binary 9s to AND-gate 326 the AND-gate is enabled. At this time the stepping motor is moving at .99 of its final pulse rate. The next pulse from the pulse multipler advances the up-down counter to zero, disabling AND-gate 326 and triggering a single shot multivibrator 327. A pulse from the single shot. multivibrator 327 passes as a down-count signal through line 328 to both decades of the up-down counter, resetting them in a manner to be described presently, so that the pulses which they receive subsequently will cause them to count down instead of up. The same pulse from the multivibrator passes over line 329 to the S input of flip-flop 301, setting this flip-flop 1 to the 1 state, with the result that AND- gates 315, 316, and 304 are disabled, while AND-gate 303 is enabledby the 1 condition on line 302. The stepping motor is now turning at a rate which permits it to receive pulses of frequency f namely, 460 p.p.s., without missing. The operation continues until a signal is given, the source of which will be mentioned presently indicating the end of the cut.

The end of the cut is signalled by the energization of switch 23 by the action of cam 31. Through normal machine controls, which are not shown or described, the table now drops and when it bottoms switch 19 is energized. When this occurs a pulse is fed through line 330 to the up-down counter (now in the zero position and set to count down), and the count changes to 99; that is to say, the multipliers K and K are now both 9's.

Through a branch line 330a the same pulse resets flip flop 301; AND gate 303 is disabled and AND gates 304,.

315, and 316 are enabled. The high speed pulse train will be multiplied by .99 and its rate will decrease 1% for each four pulses delivered from the accumulator decade 321.

At the time the two digits were set in the tens and units decades 312 and 313 of the up-down counter from the decision unit 200, the same digits were transmitted over groups of lines 331 and 332 to a storage register 333. This storage register now impresses outputs through groups of lines 334 and 335 on one pair of inputs to a coincidence detector 336, which has another pair of inputs connected by groups of. lines 337 and 338 to corresponding groups of output lines 317 and 318, respectively, of the units decade 312 and tens decade 313 of the up-down counter. When the count in the up-down counter is reduced to coincidence with the number, in this case 17, stored in the storage register 336, the coincidence is detected and an output is generated on a line 339 (8b) running to a helix cut stop matrix 340. This matrix 340 has been further conditioned by the end-of-cut signal on line 330 from switch 19, when energized, and receives a final input on line 342 from main counter 400. This counter 400 is a presettable downcounter the operation of which will be described in detail later; it will only be mentioned now that it steps down one unit in response to each pulse from either of the AND gates 303 or 304,

the pulses being passed through an OR gate 342 to the input line 343 of the counter 400. When the counter steps to the next even number, the three conditions of matrix 340 are satisfied and an output pulse is sent over line 344 to control unit 80, stopping the pulses f issuing from this unit, thereby terminating one helix cutting operation.

DETAILED DESCRIPTION OF THE UP-DOWN COUNTER The two decades 312, 313 of the up-down counter are binary-decimal counters, that is, they count in accordance with the binary progression 1, 2, 4, 8, the decimal value in each decade of the counter being equal to the sum of these weighted values, buteach decade returns to zero at the tenth input pulse, the ones decade sending a carry pulse over line 157, on reaching zero, to the tens decade.

The structure of the tens decade 313 of the up-down counter is shown in FIG. 13. As the name implies, this is a counter which can be set by a suitable input pulse, to count either up or down. The up-count pulse is delivcred from switch 34 (FIG. 3) when it is energized, that is, when it is closed by cam 35. Line 345 (FIG. 12) delivers the pulse to the counter.

The counter comprises a group of four flip-flops 346, 347, 348 and 349, and interconnecting circuitry. Each flip-flop is set to represent a I (not one) when the right hand side has an output of one, and to represent a 1 (one) when the left hand side has an output of one. As shown 

1. THE METHOD OF MACHINING A HELICAL GROOVE IN A WORK PIECE IN A MACHINE HAVING A TOOL AND A WORK-HOLDING SPINDLE, WHICH COMPRISES MOUNTING THE WORKPIECE ON THE SPINDLE TO TURN AND TO TRAVEL IN UNISON THEREWITH, GENERATING PULSES IN AN INDEPENDENT MASTER PULSE SOURCE, MOVING THE SPINDLE ALONG A PREDETERMINED PATH RELATIVE TO THE TOOL AT A SELECTED RATE IN RESPONSE TO A FRACTION OF THE NUMBER OF PULSES FROM SAID SOURCE, TO ACHIEVE AN OPERATIVE RELATION BETWEEN THE MOUNTED WORKPIECE AND THE TOOL, 